This invention relates to self exited high frequency generators in general and more particularly to an improved self exited high frequency generator of the type utilizing an oscillator tube and parallel resonant circuit with a high frequency current transformer forming a portion of the resonant circuit.
High frequency generators of the type made up of an oscillator tube and a parallel resonant circuit with a high frequency transformer in the resonant circuit for coupling the generator output to a load are known. Typically, a high frequency current transformer which does not have an iron core is used, as disclosed in German Pat. No. 1,177,702. In arrangement disclosed therein a slider arm with a contact head sliding along the primary coil and continually adjustable under load is installed within the main magnetic field generated by the transformer. This contact or adjustable tap is used as one of the two terminals of the resonant circuit. By means of adjusting the tap, a continuous matching of the high frequency generator to the load with constant good coupling and high efficiency is obtained. Although this method of matching has shown good results in practical operation, problems are encountered with regard to the physical construction of the adjustable slider arm along with the contact which slides along the primary coil and with regard to the voltage stressing of the capacitor in the resonant circuit. The capacitor, depending on the match, can have a voltage thereon which changes by a factor of two ore more.
In German Offenlegunsschrift No. 2,263,675 a high frequency transformer for an induction heating installation having a primary and a secondary winding is disclosed. In the disclosed arrangement both windings are essentially cylindrical in form and located on a common central axis. The coils are retained relative to each other in a telescopic coaxial arrangement surrounding an open central chamber. Within the central chamber a core having an outer layer of high permeability material is placed. The length of the core is essentially equal to that of the coil. To vary the output power induced in the secondary coil, the core is mounted for movement in the axial direction of the coil. This previously developed arrangement has as its primary disadvantage that, with the moving of the core, a variation in frequency takes place.
In view of these difficulties with the prior art arrangements, it can be seen that there is a need for a high frequency generator of simple physical construction which avoids the above described disadvantages and permits a continuous matching of the load and the oscillator tube.